Use of foam for firefighting in tank farms of the oil and petrochemical business – Part 2

Part One of this article described the standard incident situations at tank farm fires and offered foam as probably the most suitable extinguishing agent together with the firefighting tools mostly used. In Part Two we take a look at foam concentrate proportioning applied sciences, mobile extinguishing systems and conclude with classes learned.
NFPA eleven describes varied forms of foam focus proportioning tools. In the following, three systems are checked out that are most common. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning rate should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning rate must not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth have to be used respectively).
To assure right proportioning, the proportioner, including the proportioning rate should be tested a minimal of every year and its appropriate functioning have to be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner

The bladder tank with a proportioner is a confirmed and cost-effective technology. The bladder tank is a pressurized vessel with a bladder inside which is full of foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi precept. When the fire pumps are activated, strain is generated by the pump, inflicting supply of froth focus to the proportioner. The extinguishing water flows through the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water move.
The advantages of this technique are its easy design without shifting components and its straightforward operation. No external vitality is required, and the system is comparatively cheap.
A drawback is that the system is a pressurized vessel topic to corresponding laws such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the froth concentrate. At a given proportioning rate, the system is appropriate just for low variations within the extinguishing water circulate strain and quantity. Adding or changing particular person foam discharge gadgets is possible solely to a really limited extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated at the venturi proportioner within the extinguishing water line. The appropriate proportioning fee should be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam concentrate in the bladder tank must be changed.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with move meter

The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a flow meter in the extinguishing water flow line. When the fireplace pumps are activated, the foam concentrate pump drive and digital management system must be activated. The extinguishing water flow fee is measured by the move meter and the control system adjusts the correct foam concentrate amount by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam focus pump. If there’s a change in the circulate rate, the amount of injected foam focus is regulated by the control valve.
The system’s benefit lies in the exact proportioning of the froth concentrate, impartial of the extinguishing water pressure or circulate rate. Foam concentrate could be topped up in the course of the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system have to be activated; however, the delivered foam concentrate could be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus move rate. No premix is produced; and because the foam concentrate is handed back into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free power supply for the foam concentrate pump and the control system, as well as the need for a classy management system and the comparatively larger buying prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water move rate and the newly adjusted foam concentrate quantity. The foam quality may be compromised when continually changing working situations as foam discharge gadgets are turned on or off or modified.
Water motor with proportioning pump

The system consists of an atmospheric tank for the foam focus, a water motor installed within the extinguishing water flow line and a foam focus pump which is connected directly to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the move rate modifications, the amount of froth concentrate is tailored immediately.
The advantage of the system is its independence from exterior vitality sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water stress or circulate fee. If a piston or plunger pump is used, adjustment or calibration after installation isn’t needed because the water motor and the pump are volumetric units firmly linked to one another. Foam concentrate refilling during operation is feasible. pressure gauge 10 bar can also be capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam concentrate could be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the froth concentrate is handed again into the tank, no foam focus needs to be topped up.
The larger design and the comparatively higher purchasing costs are an obstacle of the system.
With any system, consideration should be taken under consideration for the annual testing prices, which may be considerable when it comes to substitute foam focus, disposal of premix and labour costs.
Mobile extinguishing techniques

As the stationary foam discharge gear could be damaged in intensive fires in the tank or in the dyke area and thus lose effectiveness, cell hearth monitors and foam pipes may be used.
Foam pipes

Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve solely restricted extinguishing agent flow rates and reaches.
Firefighting displays

Firefighting displays are discharge gadgets mounted on vehicles or trailers and out there in plenty of sizes. The extinguishing agent flow rate may be as a lot as 60,000 litres/min and the reach could be up to 180m if the strain of the hearth pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank to find a way to stop it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space should all the time be observed to avoid an overflow of the dyke.
Mobile hearth screens can be provided either by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the froth concentrate usually takes place through cell proportioners. This clearly factors towards the advantage of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile models out there as back-ups is shown by the following instance for the placement of displays for fireplace extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several alternatives for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which ought to have the flexibility to deal with various circulate rates to guarantee flexibility throughout extinguishing operations. Depending on the native conditions, the screens might need to maintain a minimum distance to the burning tank or might not have the flexibility to be positioned near to the tanks due to debris. In addition, it is not going to at all times be attainable to position a number of displays around the tank. It must be ensured the monitor has adequate throwing top in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the complete firefighting system is made following authorized rules as nicely as recommendations by associations like NFPA and is not looked at extra intently in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized

As talked about in the introduction to Part One of this article, plainly many authorities and firms have not realized the necessary classes from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical trade don’t happen frequently. When they do, they usually have devastating penalties. Let us keep in mind the tank farm hearth at Deer Park, Texas in March 2019 mentioned within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught hearth for yet unknown reasons. The plant had no gas warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have fixed extinguishing systems installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot very quickly however couldn’t take management over the fireplace with the tools obtainable, partially as a outcome of flammable substance was continuously leaking from the tank. Thirty-six hours after the fireplace had damaged out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of equipment and foam concentrate in addition to the preparation of a plan of action took roughly 13 hours. The fire was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt have been revamped three days, with foam concentrate and water shortages occurring within the meantime. In total, over 500,000 litres of froth focus have been used. Instead of a fireplace within the dyke space, 11 of the 15 tanks burnt down.
It could be very possible that the hearth would have been extinguished quickly if the warning systems and valves had labored and a fixed fire extinguishing system had existed. It is also possible that the fire would have been extinguished shortly if the extinguishing operation, which succeeded ultimately, had been started earlier. Both cases would have resulted in notably less harm.
Summing up, the following points should be realized at least. As far as they have not but been implemented, or just partly, they want to serve as a foundation for discussions about one’s own fire-protection idea:
Have an appropriate fire-protection idea including various scenarios which adapt to the given state of affairs frequently.
Always have a enough number of mobile extinguishing methods as a backup to fastened extinguishing methods.
Stock a suitable foam focus.
Ensure sufficient foam concentrate supply.
Ensure adequate water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing gear out there in a enough number.
Have skilled personnel available in a sufficient quantity.
Ensure a quick implementation of a suitable plan of motion.
For more info, go to www.firedos.com

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